Re: s6 xinit replacement?

[Samuel Holland <samuel@sholland.org>]

On 5/28/22 12:15 PM, Dallin Dahl wrote:
> It turns out I had the same issue as Rio, since my login shell was still
> controlling my terminal.  If I run:
> 
> exec s6-setsid X :3 vt3
> 
> while logged into tty3, I get an X display.  However, I still can't
> seem to get it to work with s6-svscan.  If I exec into s6-svscan from
> my login shell, svscan then controls the tty.  If I exec into s6-setsid
> s6-svscan, it still seems attached to the tty.  I thought that maybe
> using the tiocnotty ioctl call would free the tty for X to pick up,
> so I wrote the following wrapper program:
> 
> #include <fcntl.h>
> #include <sys/ioctl.h>
> #include <stdio.h>
> #include <unistd.h>
> 
> int main(int argc, char **argv) {
> 	int tty = open("/dev/tty", O_RDONLY);

This doesn't close the TTY. I don't know if that makes a difference.

> 	int res = ioctl(tty, TIOCNOTTY);
> 	if(!~res) perror("tiocnotty");
> 	argv++;
> 	execvp(*argv, argv);
> 	return 0;
> }
> 
> and tried to exec into that before s6-svscan, both with and without
> s6-setsid.  Unfortunately, the process immediately exits.  I don't think
> it's my wrapper program, since I can run other programs with it without
> problems, and they do indeed show up in the output of ps aux without a
> controlling terminal.
> 
> So I guess the new question is how can I free the tty after login,
> allowing X to open it and control it?

Have you tried redirecting all three standard fds elsewhere (/dev/null or a
file) when running s6-svscan? Possibly either s6-svscan or s6-supervise is doing
some fd manipulation that steals control of the TTY before X can get it. You
could also try running s6-supervise directly to narrow this down.

Regards,
Samuel